Thermal analysis of the double-melting behavior of poly(L-lactic acid)

The melting and crystallization behavior of poly(L -lactic acid) (PLLA; weight-average molecular weight = 3 × 10⁵) was studied with differential scanning calorimetry (DSC). DSC curves for PLLA samples were obtained at various cooling rates (CRs) from the melt (210 °C). The peak crystallization temperature and the exothermic heat of crystallization determined from the DSC curve decreased almost linearly with increasing log(CR). DSC melting curves for the melt-crystallized samples were obtained at various heating rates (HRs). The double-melting behavior was confirmed by the double endothermic peaks, a high-temperature peak (H) and a low-temperature peak (L), that appeared in the DSC curves at slow HRs for the samples prepared with a slow CR. Peak L increased with increasing HR, whereas peak H decreased. The peak melting temperatures of L and H [T_m(L) and T_m(H)] decreased linearly with log(HR). The appearance region of the double-melting peaks (L and H) was illustrated in a CR–HR map. Peak L decreased with increasing CR, whereas peak H increased. T_m(L) and T_m(H) decreased almost linearly with log(CR). The characteristics of the crystallization and double-melting behavior were explained by the slow rates of crystallization and recrystallization, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 25–32, 2004     

Thermal stability and nonisothermal crystallization of short fiber-reinforced poly(ether ether ketone) composites

The thermal stability of a short carbon-fiber-reinforced PEEK composite was assessed by thermogravimetry and by a Rheometrics dynamic analyzer. The results indicated that holding for 10 min at 380°C was a suitable melting condition to avoid the thermooxidative degradation under air. After proving that the heating rate of 50°C/min can be used to evaluate the crystallinity, a heating stage was used to prepare nonisothermally crystallized specimens using cooling rates from 1 to 100°C/min after melting at 400°C for 3 or 15 min. The degree of crystallinity and the melting behavior of these specimens were investigated by DSC at a heating rate of 50°C/min. The presence of three or four regions indicated that the upper melting temperature, T_m, changed with the crystallization temperature. The first region with the highest T_m, which corresponded to the cooling rate of 1°C/min, can be associated with the crystallization in regime II. There was a second region where T_m decreased as the amount of crystals formed in regime II decreased with increasing cooling rate from 5 to 20°C/min. The third region, a plateau region, corresponded to regime III condition in which the crystals were imperfect. In the fourth region, the cooling was so fast that crystallization was incomplete during the cooling for the melting condition of 400°C for 15 min. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2225–2235, 1998     

Approach to improving the toughness of TGMDA/DDS epoxy resin by blending with thermoplastic polymer powders

A series of hot-melt processable thermosetting compositions was prepared by blending N,N,N′,N′-tetraglycidyl-4,4′ -diaminodiphenyl-methane/4,4′-diaminodiphenylsulfone (TGMDA/DDS) epoxy resin and thermoplastic polymer powders with average particle size below 30 μm. The basic thermoplastic polymers were either a high T_g amorphous cardo polyimide (T_g=350°C) or commercial semicrystalline PA6 and PA12 polyamides. The resulting heterogeneous mixtures showed viscosity values below 5000 cps suitable for prepregging process. After cure, phase-separated morphologies were maintained with a rather limited interphase miscibility as demonstrated by thermomechanical analysis. Scanning electron microscope examination of fracture surfaces pointed out a strong adhesion between the powder particles and the surrounding polyepoxy network, particularly for the potentially reactive polyamide structures. Moreover, as shown by differential scanning calorimeter analysis, the crystallinity ratio of the PA6 and PA12 powders was lowered due to melting during thermal polymerization. The fracture toughness properties of the powder-containing materials were compared with those of a fully miscible cardo polyimide–TGMDA/DDS blend coming from an homogeneous resin composition. The best improvement in fracture energy was obtained for the powder-modified resins. The most effective composition filled with 16 wt% of powdered polyimide exhibited a fourfold increase in G_IC (388 J/m² versus 100 J/m²) without compromising the epoxy thermomechanical stability (T_g=227°C versus 223°C).     

Multiple melting behavior of poly(butylene succinate). II. Thermal analysis of isothermal crystallization and melting process

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights (MWs) of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were isothermally crystallized at various crystallization temperatures (T_c) ranging from 70 to 97.5 °C. The T_c dependence of crystallization half‐time (τ) was obtained. DSC melting curves for the isothermally crystallized samples were obtained at a heating rate of 10 K min⁻¹. Three endothermic peaks, an annealing peak, a low‐temperature peak L, and a high‐temperature peak H, and an exothermic peak located between peaks L and H clearly appeared in the DSC curve. In addition, an endothermic small peak S appeared at a lower temperature of peak H. Peak L increased with increasing T_c, whereas peak H decreased. The T_c dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of T_c. T_m(L), T_re, and ΔH increased almost linearly with T_c, whereas T_m(H) was almost constant. The maximum rate of recrystallization occurred immediately after the melting. The mechanism of the multiple melting behavior is explained by the melt‐recrystallization model. The high MW samples showed similar T_c dependence of τ, and τ for the lowest MW sample was longer than that for the others. Peak L increased with MW, whereas peak H decreased. In spite of the difference of MW, T_m(L), T_m(H), and T_re almost coincided with each other at the same T_c. The ΔH values, that is crystallinity, for the highest MW sample were smaller than those for the other samples at the same T_c. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2039–2047, 2005     

Studies on surface molecular motion of oligomeric polystyrene by differential scanning calorimetry

There are many studies on the surface molecular motion of polymer films [ 1 ], but no report on surface thermal properties of polymer because of experimental difficulties. The thermal property of oligomeric polystyrene (PS) was investigated by differential scanning calorimetry (DSC) in the present study. In order to increase the ratio of surface area to volume of PS particles, the DSC samples were prepared by mechanically grinding mixtures of PS and Al₂O₃ powders. The grinding mixtures of these powders with low particle size showed a transition at a low temperature of 14–17 °C (much lower than the bulk glass transition temperature, T_g), and this low‐temperature transition was dependent on the size of PS particles. This transition seems to result from the surface molecular motion of the activated surface layer of PS. Copyright © 2000 John Wiley & Sons, Ltd.     

Multiple melting behavior of poly(butylene succinate). I. Thermal analysis of melt‐crystallized samples

The multiple melting behavior of poly(butylene succinate) (PBSu) was studied with differential scanning calorimetry (DSC). Three different PBSu resins, with molecular weights of 1.1 × 10⁵, 1.8 × 10⁵, and 2.5 × 10⁵, were cooled from the melt (150 °C) at various cooling rates (CRs) ranging from 0.2 to 50 K min^?1. The peak crystallization temperature (T_c) of the DSC curve in the cooling process decreased almost linearly with the logarithm of the CR. DSC melting curves for the melt‐crystallized samples were obtained at 10 K min^?1. Double endothermic peaks, a high‐temperature peak H and a low‐temperature peak L, and an exothermic peak located between them appeared. Peak L decreased with increasing CR, whereas peak H increased. An endothermic shoulder peak appeared at the lower temperature of peak H. The CR dependence of the peak melting temperatures [T_m(L) and T_m(H)], recrystallization temperature (T_re), and heat of fusion (ΔH) was obtained. Their fitting curves were obtained as functions of log(CR). T_m(L), T_re, and ΔH decreased almost linearly with log(CR), whereas T_m(H) was almost constant. Peak H decreased with the molecular weight, whereas peak L increased. It was suggested that the rate of the recrystallization decreased with the molecular weight. T_m(L), T_m(H), T_re, and T_c for the lowest molecular weight sample were lower than those for the others. In contrast, ΔH for the highest molecular weight sample was lower than that for the others. If the molecular weight dependence of the melting temperature for PBSu is similar to that for polyethylene, the results for the molecular weight dependence of PBSu can be explained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2411–2420, 2002     

High-temperature aging of Halar film. II. Analysis of melting behavior

Melting behavior of an experimental Halar film, a predominantly alternating 1:1 copolymer of ethylene (E) and chlorotrifluoroethylene (CTFE), has been studied. Differential scanning calorimetry (DSC) reveals single or double melting peaks, depending upon the thermal history. The lower-temperature melting peak T_m1 is produced only by the thermal treatment and shows a strong dependence on annealing time and temperature. On the basis of the DSC and x-ray data it can be suggested that T_m1 represents the melting of relatively small crystallites formed upon annealing. The higher-temperature melting peak T_m2 is always shown at 238°C. (Note: the specification for commercial Halar product is 240°C. The slightly lower melting temperature reported in this study is probably due to the fact that we are dealing with an experimental melt-processed material.) On the basis of the heating rate study we propose that Halar crystallizes with stable crystals (T_m2 = 238°C) regardless of the crystallization conditions, i.e., quenching, slow cooling, or even annealing. Crystals of Halar have a heat of fusion of approximately 35 cal/g or 146 kJ/kg. Detailed analysis of the melting behavior of Halar is presented.     

Calorimetric analysis of the multiple melting behavior of melt-crystallized poly(l-lactic acid) with a low optical purity

The polymorphous crystallization and multiple melting behavior of poly(l-lactic acid) (PLLA) with an optical purity of 92 % were investigated after isothermally crystallized from the melt state by wide-angle X-ray diffraction and differential scanning calorimetry. Owing to the low optical purity, it was found that the disordered (α′) and ordered (α) crystalline phases of PLLA were formed in the samples crystallized at lower (<95 °C) and higher (≥95 °C) temperatures, respectively. The melting behavior of PLLA is different in three regions of crystallization temperature (T _c) divided into Region I (T _c < 95 °C), Region II (95 °C ≤ T _c < 120 °C), and Region III (T _c ≥ 120 °C). In Region I, an exothermic peak was observed between the low-temperature and high-temperature endothermic peaks, which results from the solid–solid phase transition of α′-form crystal to α one. In Region II, the double-melting peaks can be mainly ascribed to the melting–recrystallization–remelting of less stable α crystals. In Region III, the single endotherm shows that the α crystals formed at higher temperatures are stable enough and melt directly without the recrystallization process during heating.     

Synthesis and characterization of a series of wholly aromatic copolyesters containing 2‐(α‐phenylisopropyl)hydroquinone moiety

Two series of new wholly aromatic thermotropic copolyesters containing the 2‐(α‐phenylisopropyl)hydroquinone (PIHQ) moiety have been synthesized and their basic properties such as glass transition temperature (T_g), melting temperature (T_m), thermal stability, crystallinity, and liquid crystallinity were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), and wide‐angle X‐ray diffractometry (WAXD) and on a polarizing microscope. The first series was prepared from acetylated PIHQ, terephthalic acid (TPA), and 2,6‐naphthalenedicarboxylic acid (NDA), and the second series from acetylated PIHQ, TPA, and 1,1′‐biphenyl‐4,4′‐dicarboxylic acid (BDA). The T_g values (152–168°C) of the two series are not much different, although the values for the first series appear slightly higher. The T_m values (287–378°C) and the degree of crystallinity of the first series are appreciably greater than those of the second series. Such differences can be explained by the geometric structure of NDA and BDA moieties. All of the present polyesters are thermotropic and nematic. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 881–889, 1999     

Dipyrido[3,2-a:2′,3′-c]phenazine-Tethered Oligo-DNA: Synthesis and Thermal Stability of Their DNA⋅DNA and DNA⋅RNA Duplexes and DNA⋅DNA⋅DNA Triplexes

Dipyrido[3,2-a:2′,3′-c]phenazine (dppz) derivatives were conjugated to 9-mer and 18-mer DNA (ODN) at a site without nucleobase, either at the 5′- or 3′-end or at a internucleotide position, via linkers of 7, 12, or 18 atoms lengths. These dppz-linked ODNs were synthesized using novel backbone glycerol phosphoramidites: Glycerol, serving as artificial nucleoside without nucleobase, was modified to amines 10 , 23 , and 24 , which were suitable for the subsequent key reaction with dppz-carboxylic acid 3 (Schemes 2 and 3). The products of these reactions (see 5 – 7 ) were then transformed to the standard phosphoramidite derivatives (see 27 , 29 , and 30 ) or used for loading on a CPG support (see 28 , 31 , and 32 ). The dppz-modified ODNs were subsequently assembled in the usual manner using automated solid-phase DNA synthesis. The 9-mer ODN-dppz conjugates 35 – 43 were tested for their ability to form stable duplexes with target DNA or RNA strands (D11 ( 60 ) or R11 ( 61 )), while the 18-mer ODN-dppz conjugates 48 – 56 were tested for their ability to form stable triplexes with a DNA target duplex D24⋅D24 ( 62 ) (see Tables 1 and 2). The presence of the conjugated dppz derivative increases the stability of DNA⋅DNA and DNA⋅RNA duplexes, typically by a ΔT_m of 7.3 – 10.9° and 4.5 – 7.4°, respectively, when the dppz is tethered at the 5′- or 3′-terminal (Table 2). The dppz derivatives also stabilize triplexes when attached to the 5′- or 3′-end, with a ΔT_m varying from 3.8 – 11.1° (Table 3). The insertion of a dppz building block at the center of a 9-mer results in a considerably poorer stability of the corresponding DNA⋅DNA duplexes (ΔT_m=0.5 to 4.2°) and DNA⋅RNA duplexes (ΔT_m=−1.5 to 0.9°), while the replacement of one interior nucleotide by a dppz building unit in the corresponding 8-mer ODN does not reveal the formation of any duplex at all. Different types of modifications in the middle of the 18-mer ODN, in general, do not lead to any triplex formation, except when the dppz derivative is tethered to the ODN through a 12-atom-long linker (Entry 9 in Table 3).     

Thermodynamic and kinetic behaviour of salicylsalicylic acid

The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC). The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10°C min^-1. The melting peak showed an onset at T _on = 144°C (417 K) and a maximum intensity at T _max = 152°C (425 K), while the onset of the glass transition signal was at T _on = 6°C. The melting enthalpy was found to be Δ_mH = 28.9±0.3 kJ mol^-1, and the heat capacity jump at the glass transition was ΔC _P = 108.1±0.1 J K^-1mol^-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed the determination of the activation energy at the glass transition temperature (245 kJ mol^-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as Δ_fH_m ^o(C₁₄H₁₀O₅, cr) = - (837.6±3.3) kJ mol^-1, by combustion calorimetry. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wholly aromatic thermotropic liquid crystalline polyesters of 4,4′-biphenol,substituted biphenols,and 1,1′-binaphthyl-4,4′-diol with 3,4′-benzophenone dicarboxylic acid

Wholly aromatic, thermotropic homopolyesters, derived from 4,4′-biphenol, substituted biphenols, or 1,1′-binaphthyl-4,4′-diol and 3,4′-benzophenone dicarboxylic acid, and two copolyesters, each of which contained 30 mol % of 6-hydroxy-2-naphthoic acid, were prepared by acidolysis polycondensation reactions and characterized for their liquid crystalline properties. The solubility behavior of these polymers has also been investigated. The two homopolymers of phenyl-substituted biphenols with 3,4′-benzophenone dicarboxylic acid were soluble in many common organic solvents. All of the homopolymers had lower T_m/T_f values than those with terephthalic acid, which was attributed to the incorporation of the asymmetric 3,4′-benzophenone dicarboxylate units in a head-to-head and head-to-tail fashion along the polyester chain. Two copolymers had lower T_m values than those of the respective homopolymers, as expected. They formed nematic phases which persisted up to 400°C, except those of phenyl-substituted biphenols with 3,4′-benzophenone dicarboxylic acid. Each of these two polymers also exhibited an accessible T_i transition, and had a broad range of LC phase. They had glass transition temperatures, T_g, in the range of 139-209°C and high thermal stabilities in the temperature range of 465-511°C. © 1995 John Wiley & Sons, Inc.     

Micellization to gelation of a triblock copolymer in water: Thermoreversibility and scaling

Aqueous solutions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer, Pluronic F108 (PEO₁₃₃PPO₅₀PEO₁₃₃), ranging from 1 to 35 wt %, were studied with differential scanning microcalorimetry and rheology. The thermoreversible micellization and gelation were examined through a heating process and a subsequent cooling process at a fixed rate of 1 °C/min. The critical micellization temperature (CMT), determined by the onset temperature of the endothermic peak in the heating process, was a decreasing function of the F108 concentration. A small secondary endothermic peak appeared only when the polymer concentration was 22.5 wt % or higher, indicating that there was a sol–gel transition but that the gelation was a nearly athermic process. Upon heating, an abrupt increase was observed in both the dynamic storage modulus (G′) and dynamic loss modulus (G″) within a narrow temperature range. T_G′, the temperature for the transition in G′, was a linear decreasing function of the polymer concentration and different from CMT. T_G′ tended to approach CMT with an increasing F108 concentration. Beyond this transition, G′ reached a plateau, and the plateau increased in height and broadened with the polymer concentration. The value of G′ at 70 °C (G′₇₀) could be approximately scaled with concentration c by G′₇₀ ∝ c^7.3. In addition, the definition for a gel to obey G′ > G″ was valid only when c was greater than 22.5 wt %, and this was in agreement with the secondary endothermic peak found with differential scanning calorimetry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2014–2025, 2004     

Einfluß der thermischen Vorgeschichte auf die Phasenumwandlungen von Dipalmitoyllecithin/Wasser-Mischungen

1. The influence of the thermal pretreatment (first and second heating run, annealing process) on the phase transition temperaturesT _m, enthalpiesΔ¯H _m and the specific heatc _sp of 1,2-dipalmitoyllecithin-water-mixtures was studied by differential scanning calonmetry.
2. The differences in theT _m- andΔ¯H _m-data of the main transition of the first and second heating run were found in the concentration rangex ^w<0,75. In the concentration rangex _W>0.75 these differences disappear.
3. The annealing process of a 1,2-dipalmitoyllecithin-water-mixturex _W=0,89 leads to a splitting of the main transition peak in two separate peaks with a different shape. This behaviour may imply that 1,2-dipalmitoyllecithin coexists in two different hydration states.

     

Stepwise annealing of poly(butylene terephthalate)

Annealing of poly(butylene terephthalate) (PBT) was studied by differential scanning calorimetry (DSC) and small angle X‐ray scattering (SAXS) measurement. A PBT sample was annealed at a recrystallization temperature where recrystallization occurs with a maximum rate in the heating process of the sample. In the subsequent annealing steps, the annealed sample was annealed repeatedly at the recrystallization temperatures, and the stepwise annealing sample was obtained. Peak melting temperature (T_m) and sharpness of DSC peak of the stepwise annealing sample increased with the annealing step. A high melting‐temperature sample was obtained in a short time, and T_m increased up to 238.5°C which is higher than all the T_m values that appear in the literature. The long period calculated from SAXS curves of the stepwise annealing sample increased with the annealing step. The increase of crystallite size and perfection of the crystal in the stepwise annealing process is suggested. Annealing experiment indicated that T^°_m should be higher than about 235°C. T_m increased linearly with the annealing temperature of the final step in the stepwise annealing (T_a). The equilibrium melting temperature (T^°_m) for PBT was estimated to be 247°C by the application of a Hoffman–Weeks plot to the relation between T_m vs. T_a. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2420–2429, 1999     

Polymorphism and melt crystallisation of racemic betaxolol, a β-adrenergic antagonist drug

We report the polymorphic behaviour, in melt cooling experiments, of racemic betaxolol, a low aqueous solubility selective β₁-adrenergic antagonist drug with a flexible molecular structure. A multidisciplinary approach is employed, using thermal analysis (differential scanning calorimetry, polarised light thermomicroscopy), spectroscopic methods (infrared spectroscopy, magic angle spinning ¹H NMR) and X-ray powder diffraction. A glass phase is obtained, T _g ~ ?10 °C, on cooling the melt, unless the cooling rate is ≤0.5 °C min^?1, while a new metastable form, polymorph II, T _fus = 33 °C, is generated in subsequent heating runs in a two step process. Although either partial crystallisation from the melt in the first step or the formation of an intermediate, metastable, low ordered phase may explain these observations, our results favour the second hypothesis. The stable polymorph I, T _fus = 69 °C, which crystallizes on further heating after form II melting, has also been obtained either from polymorph II or from the molten phase, on standing at 25 °C. The racemic betaxolol crystalline phases are found to exhibit some degree of disorder.     

Lamellar thickening in nascent poly(acrylonitrile) upon annealing

No systematic study has been reported on the lamellar thickening in atactic poly(acrylonitrile) (PAN) upon annealing because PAN, in the form of solution‐cast films or their drawn products, generally shows no small‐angle X‐ray scattering (SAXS) maximum corresponding to the lamellar thickness. In this work, PAN crystals were precipitated during the thermal polymerization of acrylonitrile in solution. The nascent PAN film, obtained by the filtration of the crystal suspension, exhibited a clear SAXS maximum revealing the lamellar structure. The lamellar thickening upon annealing of the nascent PAN films was studied in the temperature range 100–180 °C, where the degradation was minimal, as confirmed by the absence of an IR absorption band at 1605 cm⁻¹ ascribed to the cyclized nitrile groups. Above 190 °C, the degradation of the samples was significant, and the SAXS became too broad to determine the scattering maximum. The long period was significantly affected by the annealing time (t_a) and the temperature (T_a). Depending on t_a, three stages were observed for the lamellar thickening behavior. The lamellar thickness stayed constant in stage I (t_a = 0.5–3 min, depending on T_a), rapidly increased in stage II (t_a = 0.5–8 min), and stayed at a constant value characteristic for each T_a at yet longer t_a's in stage III. The lamellar thickness characteristic for T_a increased rapidly with increasing T_a at 165 °C (or higher), which was 152 °C lower than the estimated melting temperature of PAN (T_m = 317 °C). A possible mechanism for such lamellar thickening in PAN far below the T_m is discussed on the basis of the enhanced chain mobility in the crystalline phase above the crystal/crystal reversible transition at 165–170 °C detected by differential scanning calorimetry and wide‐angle X‐ray diffraction. The structural changes associated with annealing are also discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2571–2579, 2000     

Studying Cu2–xSe phase transformation through DSC examination

The thermal effect accompanying the transition of Cu_2–xSe into a superionic conduction state was studied by non-isothermal measurements, at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C min^–1). During heating the peak temperature (T_p) remains almost stable for all values of β, (136.8±0.4°C for Cu₂Se and 133.0±0.3°C for Cu_1.99Se). A gradual shift of the initiation of the transformation towards lower temperatures is observed, as the heating rate increases. During cooling there is a significant shift in the position of the peak maximum (T_p) towards lower temperatures with the increase of the cooling rate. A small hysteresis is observed, which increases with the increase of the cooling rate, β. The mean value of transformation enthalpy was found to be 30.3±0.8 J g^–1 for Cu₂Se and 28.9±0.9 J g^–1 for Cu_1.99Se. The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)^n(1+kcatX), with activation energy E=175 kJ mol^–1, exponent value n equal to 0.2, logA=20 and log(k_cat)= 0.5.     

Fractionated and Confined Crystallization of Polybutene-1 in Immiscible Polypropylene/Polybutene-1 Blends

In this work,the crystallization of immiscible polypropylene(PP)/polybutene-1(PB)blends,in particular the effect of crystal morphology of PP(HTC,high Tm component)on the subsequent crystallization behavior of PB(LTC,low Tm component)was studied.Herein,we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP.Crystallization of PP at different crystallization temperatures brought about different PP crystal morphologies and PB was segregated and confined at different locations.Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature.As temperature continued to fall below Tm of PB,the fractionated and confined crystallization of PB occurred in the framework of PP spherulites,reflected by the decreased crystallization temperature(Tc)of PB and the formation of form I′beside form II.Notably,if PP previously crystallized at high Tc,fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.     

Differential scanning calorimetric examination of the human skeletal muscle in a compartment syndrome of the lower extremities

The compartment syndrome—conditions of elevated intramuscular pressure—is one of the most serious complications of the injuries of the lower extremities. Early diagnosis is important, as delayed treatment leads to significant complications. The diagnosis of compartment syndrome is most commonly made by clinical examination and direct measurement of the intra-compartmental pressure. Our hypothesis was that in different stages of compartment syndrome there is a clear pathological abnormality in the tissue elements of the affected muscles, which is responsible for seriousness of the disease, and could be monitored besides the classical histological methods by differential scanning calorimetry. The thermal denaturation of different parts of human samples was monitored by a SETARAM Micro DSC-II calorimeter. All the experiments were performed between 0 and 100 °C. The heating rate was 0.3 K/min. DSC scans clearly demonstrated significant differences between the different types and conditions of samples (control: T_m = 55.5; 59.9 °C and ΔH_cal = 0.52 J/g, Gr. I.: T_m = 58.1; 62.2 °C and ΔH_cal = 0.28 J/g, Gr. II.: T_m = 57.45; 61.5 °C and ΔH_cal = 0.24 J/g, Volkmann’s ischemic contracture T_m = 57.75; 61.8; 65.8 °C and ΔH_cal = 0.74 J/g). These observations could be explained with the structural alterations caused by the biochemical processes. The heat capacity change between native and denatured states of muscle samples was significant, indicating significant water loosing during denaturation, but independent from the structural alterations.